Let your batter rest for at least 30 minutes. The clumps will even out when the flour swells.
Warm your oven to 435 F (225 C)
Melt the butter on the sheet pan in the oven. Take out the pan and give it a swirl so the butter spreads out evenly.
Pour your batter on the hot pan. Bake for 30-40 minutes until nicely browned.
Giant bubbles will form on the pannukakku while baking. You can break them while baking, so you get a more even color.
Serve slightly cooled with strawberry jam.
Video
Notes
Nutrition for one piece made in whole milk: 9 g fat, 27 g carbs, 0,9 g fiber, 8,5 g protein. You can also use baking paper if you want to protect your baking tray. Stores in the fridge for 3-4 days.